Chemical substances for medical drugs or the like are produced by synthesizing the substances in solvents or extracting them to solvents and removing the unnecessary solvents by evaporation. The solvents, if necessary, may be completely evaporated so that the substances are crystallized, that is, dried (see, for example, Patent Documents 1 and 2).
The solvent used for producing a chemical substance is appropriately selected depending on the chemical substance desired, and the optimal conditions (treatment temperature, evaporation rate, treatment time, etc.) for evaporation of the solvent are varied depending of the chemical substance.
Before the industrial production of such a chemical substance, in general, the optimal evaporation conditions being predetermined from investigation for the evaporation pattern of the solvent and the state of the resulting chemical substance, under different evaporation conditions determined by varying the treatment temperature, the evaporation rate of the solvent, the treatment time, the degree of vacuum, and other conditions, using laboratory equipment, the chemical substance was produced.
One of the conventional techniques for determining the optimal evaporation conditions according to object containing a single-component solvent is a mass measurement technique in which the evaporation rate of the solvent is measured by measuring the changes in mass of the object on a balance with elapsed time. If the object contains several types of solvent, a break technique is employed for the determination of the evaporation rate of the solvent. In the break technique, the solvents in an object are evaporated and removed by evacuating an airtight container, such as a model of dryer, containing the object with a vacuum pump. In the course of this process, the vacuum pump is suspended several times so that the pressure in the airtight container returns to atmospheric pressure, and part of the object in the airtight container is sampled and weighed on a balance at each time. The sample is dissolved in an appropriate solvent, and the content of each residual solvent is measured by gas chromatography. Then, the object is vacuum-dried again. This procedure is repeated, and the latest measurement results are compared with the previously obtained measurement results. The evaporation rate of each solvent is obtained from the difference between the contents.
Patent Document 1: Japanese Unexamined Patent Application Publication No. 2000-80072
Patent Document 2: Japanese Unexamined Patent Application Publication 6-87802